In a vehicle, a Multiple Displacement System (MDS) employs a means of activating and deactivating cylinders in a gasoline engine to improve fuel economy. For example, in an MDS vehicle utilizing an eight cylinder engine (i.e. V8 mode), the MDS computes a requested power by an operator of the vehicle needed to perform and maintain engine speed and vehicle load. The requested power is determined based on a position of an accelerator pedal depressed by the operator. If the MDS decides that the engine can operate and satisfy the requested power of the operator utilizing four of the eight cylinders (i.e. V4 mode), then the MDS deactivates four selected cylinders in the engine, producing less power and energy in the deactivated cylinders. While in V4 mode, if the operator changes the requested power of the engine and the engine cannot deliver the requested power in V4 mode, the MDS reactivates the previously deactivated four cylinders and transitions from V4 mode to V8 mode. In addition to monitoring the power requested by the operator, the MDS monitors other environmental parameters and conditions within the vehicle in order to determine whether to deactivate or activate cylinders in the engine.
One method and system of deactivating and activating cylinders utilizes a decoupling mechanism in a lifter, hydraulically actuated by oil pressure (i.e. an electro-hydraulic system). An engine oil pump supplies oil under pressure to an electro-hydraulic solenoid valve located within an oil flow control valve. The electro-hydraulic solenoid valve controls the oil pressure to a locking mechanism in a lifter by adding and removing the oil pressure. When a camshaft is on its base circle and the oil pressure in a lifter control gallery rises, the locking mechanism deactivates and decouples from the camshaft. Once the lifter decouples from the camshaft, both an intake valve and an exhaust valve close sealing the cylinder such that no air or fuel flows into or out of the cylinder, causing a piston in the cylinder to deactivate. In order to reactivate the cylinder, voltage is removed from the electro-hydraulic solenoid valve causing the oil flow control valve to close and reduce the oil pressure in the lifter control gallery. Thus, the electro-hydraulic system's behavior is a direct function of the oil pressure and an amount of air contained within an oil system (i.e. oil aeration) of an engine.
One element contributing to a phenomenon of increasing the amount of oil aeration in the oil system is engine speed. As engine speed increases in the vehicle, oil contained in an oil pan of the engine becomes agitated around by a crankshaft, causing an undesirable amount of oil aeration that then travels from the oil pan throughout the oil system. When the oil system contains desirable amounts oil aeration and oil pressure, activating and deactivating cylinders in the engine is a repeatable and accurate process. However, if an undesirable amount of oil aeration or oil pressure exists, the process of activating and deactivating cylinders is nonrepeatable and inaccurate.